Electrical welding clamp comprising a mechanical device for indexing and de-indexing

ABSTRACT

The welding gun includes an electrically driven welding clamp comprising a fixed indexed arm and a mobile arm, respectively provided with an electrode, and a device for indexing and de-indexing locking and releasing the clamp movement relative to the welding plane. The device for indexing and de-indexing includes a mechanical device arranged to ensure the locking and the releasing of the clamp movement, while the clamp is opening/closing, by the action of an electrical device controlling the opening and closing of the clamp.

FIELD OF THE INVENTION

The present invention relates to an electric welding gun comprising adevice permitting indexing and de-indexing, which is to say the lockingand the unlocking of the movement of the clamp, for example the rotationin the case of a clamp about X or the translation in the case of a clampalong J, relative to its support, for example an arm of a robot on whichthe clamp is mounted.

BACKGROUND OF THE INVENTION

A welding cycle is comprised of three phases: approach, welding anddisengagement. During the welding phase, a welding clamp must be able toundergo a movement for example opening and closing, relative to therobot so as to adapt to the plates to be assembled, in particular duringapproach which corresponds to the insertion and superposition of the twopieces to be welded between the electrodes and the clamp and theestablishment of a stabilized force of the two electrodes creating anelectric circuit.

Once welding is completed, the clamp is then opened and brought by therobot to another point where welding is to be carried out.

In the course of these movements, in particular to emplace the weldinggun relative to the plates to be assembled, the movement of the clamp,which is open, can become troublesome and prevent a precise path andpositioning of the assembly. Thus, so as to optimize the cycle time ofthe robot, the latter always move along two different axes at itsmaximum speed. Because of this, during given accelerations of the robot,the welding gun tends to oscillate.

Also, to avoid substantial inertial phenomena and to avoid the gunturning because of acceleration imparted by the robot, the movement ofthe assembly of the clamp is momentarily locked by an indexing system.Also, most of the welding clamps are provided with an index systemhaving an influence on the clamp during its displacement from one workstation to another, for example.

The electric motor-driven welding clamps generally used, have anindexing and de-indexing system constituted by a jack of which theextended position of the rod permits blocking the clamp and of which theretracted position of the rod frees the movement of the clamp so as topermit self-centering of the electrodes on a plate to be assembledduring approach, and this without imparting force to the plates. So asto promote self-centering, the clamp comprises balancing springspermitting giving to the clamp a balanced position about its weldingplane.

However, in the case of electric motorized welding clamps, the presenceof the jack requires, in addition to the electric motor circuit of theclamp, the presence of a compressed air circuit as well as all theelements associated therewith, namely tubing, a compressor, etc.

It is thus necessary to provide two different types of supply.

SUMMARY OF THE INVENTION

The present invention accordingly seeks to overcome these drawbacks byproviding an electric welding gun having an electric motorized weldingclamp in which the locking and unlocking device of the movement of thewelding clamp relative to the welding plane, does not need a pneumatic,hydraulic or other supply.

To this end, the present invention has for its object an electricwelding gun having an electric motorized welding clamp comprising afixed indexed arm and a movable arm, provided respectively with anelectrode, as well as an indexing and de-indexing device locking andunlocking the movement of the clamp relative to the welding plane. Theindexing and de-indexing device comprises mechanical means arranged toensure locking and unlocking of the movement of the clamp, in the courseof the opening/closing movements of the clamp, under the influence ofelectrical control means for opening and closing the clamp.

Because of this, at the end of a welding phase, during opening of theclamp by the electrical control means, the mechanical means act on theclamp so as to index it, while conversely, an actuation of theelectrical control means in the direction of closing the clamp resultsin driving the mechanical means to de-index the clamp.

A welding gun according to the invention can thus have an X clamp aswell as a J clamp.

In the case of an X clamp, according to a preferred embodiment, themechanical means of the indexing and de-indexing device of the clamp areconstituted by a cam, a rod and a roller, the cam being mountedrotatably about its axis of securement on an ear of the selected fixedarm of the clamp, the rod having one end mounted rotatably about itsaxis of connection with the cam, the connection axis being parallel tothe axis of securement of the cam and spaced from the latter, and oneend mounted rotatably about a drive trunnion whose longitudinal axis isalso parallel to the axis of rotation of the cam, the drive trunnionbeing itself in sliding pivotal connection with the ear of the secondarm of the required movable clamp, the roller being itself secured tothe articulation of the clamp and adapted to coact with the profile ofthe cam.

Preferably, the roller is mounted, by means of a support of the indexingdevice, secured to the articulation of the clamp, the axis of the rollerbeing parallel to the axis of securement of the cam, the roller beingadapted to roll along the profile of the cam and the roller beingmoreover mounted slidably relative to its support, the sliding intranslation being limited by resilient return means such as anelastomeric member.

The cam has a profile defined by different radii different diameters ofthe cam and, when the roller rolls along the greater diameter of thecam, the arms of the clamp having a movement of rotation about thearticulation of the clamp, index themselves.

A welding gun according to the invention therefore has only a singleelectrical supply and it is thus not necessary to provide a pneumatic orhydraulic supply for the indexing and de-indexing device. There can thusalso be omitted all the circuits and components concerned with anothersupply such as a pneumatic supply for example, the tubing, a compressor,etc.

Preferably, a welding gun according to the invention has moreoveradditional safety to the extent that, in the case of the absence ofenergy supply to the clamp, the clamp and in particular its indexing andde-indexing device remain in position and the clamp remains manuallyusable.

Moreover, there is obtained a welding gun in which the speed of indexingand de-indexing does not depend on the speed of a jack but on the speedof the electric motor actuating the clamp. Furthermore, the rollerrolling on the cam leads to gentle indexing, in contrast to a jack,which is abrupt.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail using the exampleof embodiment of an X clamp with reference to the accompanying drawing,in which:

FIG. 1 is a side cross-sectional view of an indexing and de-indexingdevice of the welding gun according to the invention, and

FIG. 2 is a plan view of the device according to FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In the case of an electric motorized X welding clamp, the lattercomprises a fixed indexed arm 5 and a movable arm, the indexing orde-indexing device acting on the assembly of the clamp so as to lock ornot the rotation relative to the arms.

The indexing and de-indexing device comprises a cam 1, a rod 2 and aroller-resilient return system 3.

The ear of the support of the necessary fixed arm 5 of the clamp has afinger 4 constituting the axle of the cam 1 and on which is rotatablymounted the cam 1.

One end of the rod 2 coacts with the cam 1 by means of a connectionmember 7 secured to the lower surface of the cam 1, preferably adjacentthe peripheral edge of the cam 1, and having an axle 6, parallel to thefinger 4, on which the end 2 a of the rod 2 is rotatably mounted.

The second end 2 b of the rod 2 is rotatably mounted about a drivetrunnion 8 which is in pivotal sliding connection with the ear of theother arm of the required movable clamp.

The drive trunnion 8 is generally constituted by a nut slidably mountedalong a screw coupled to the reducer of the electric motor of the clamp.

The roller 3 is mounted by means of a support of the indexing device,secured to the articulation of the clamp, the axis of the roller 3 beingparallel to the axis of the finger 4 on which is mounted the cam 1, theroller 3 being adapted to roll along the profile of the cam.

Moreover, the roller 3 is slidably mounted relative to its support, thesliding in translation being limited by a resilient return means such asan elastomeric member.

During opening actuation of the clamp, the trunnion 8 drives the rod 2which impresses on the cam 1 a rotative movement. As a function of thedifferent diameters of the cam 1, the roller 3 rolls on the cam 1. Thearms of the clamp having a rotative movement about the articulation ofthe clamp, they index themselves when the roller 3 rolls on the largestdiameter of the cam 1. During closing of the clamp, it is the reversemovement which takes place.

Thus, when the clamp is opened after a welding phase, the clamp indexesitself and afterward the movable arm of the clamp is located at about 5mm relative to the theoretical welding plane. Preferably, at thebeginning of indexing, the distance between the electrodes is thus 10 mmand at the end of indexing 15 mm. The clamp remains indexed duringcomplete opening.

The dimension of the different elements constituting the index andde-indexing device is determined for each size of clamp as a function ofthe desired size of the intervals between the electrodes of the gun.

What is claimed is:
 1. An electric welding gun comprising: an electric motorized welding clamp with a fixed indexed arm and a movable arm, each of the fixed arm and movable arm being provided with an electrode, an indexing and de-indexing device locking and unlocking the movement of said clamp relative to a welding plane, said indexing and de-indexing device comprising a mechanical means arranged to ensure the locking and the unlocking of the movement of said clamp, in the course of opening and closing movements of said clamp, and an electric control means connected to said mechanical means for opening and closing said clamp.
 2. The welding gun according to claim 1, wherein said welding clamp comprises a J clamp.
 3. The welding gun according to claim 1, wherein said welding clamp comprises an X clamp.
 4. The welding gun according to claim 3, wherein said mechanical means of said indexing and de-indexing device comprises a cam, a rod and a roller, said cam being mounted rotatably about its axis of securement on an ear of said fixed arm of said clamp, said rod having one end mounted rotatably about its connection axis with said cam, said connection axis being parallel to the axis of securement of said cam and spaced from the latter, and one end mounted rotatably about a drive trunnion whose longitudinal axis is also parallel to the axis of rotation of said cam, said drive trunnion being in sliding pivotal connection with the ear of the second arm of the movable clamp, said roller being itself secured to the articulation of said clamp and adapted to coact with the profile of said cam.
 5. The welding gun according to claim 4, wherein said cam has different diameters, the largest diameter of said cam corresponding to the indexing of said clamp.
 6. The welding gun according to claim 4, wherein said axis of securement of said cam comprises a finger secured to the ear of said fixed arm of said clamp.
 7. The welding gun according to claim 4, wherein the end of said rod coacts with said cam by a connection member secured to the lower surface of said cam and having an axis on which the end is rotatably mounted.
 8. The welding gun according to claim 4, wherein said roller is mounted, by a support of said indexing device, secured to the articulation of said clamp, the axis of said roller being parallel to the axis of securement of said cam, said roller being adapted to roll along the profile of said cam and said roller being moreover mounted slidably relative to its support, the sliding in translation being limited by a resilient return means.
 9. The welding gun according to claim 4, wherein said drive trunnion comprises a nut slidably mounted along a screw coupled to the reducer of the electric motor of said clamp. 